This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-397445 filed on Dec. 27, 2001.
1. Field of the Invention
The present invention relates to an intake control system of a multi-cylinder internal combustion engine, the intake control system being capable of controlling quantity of intake air for each cylinder by controlling opening and closing of intake control valves disposed in respective intake passages of the engine. More specifically, the present invention relates to an intake control system that controls the intake quantity for each cylinder in order to regulate idling rotation speed during an idling operation of an internal combustion engine.
2. Description of Related Art
Conventionally, a known intake control system has intake control valves disposed in intake passages of an internal combustion engine and controls quantity of intake air for each cylinder by controlling opening and closing of each intake control valve in accordance with rotation of the engine, besides a throttle valve disposed in the engine.
In such an intake control system, the intake control valves are controlled open or close by actuators respectively and independently. Therefore, it is possible to prevent back flow of the intake air, which occurs in an intake stroke when an engine rotation speed is in a low speed range, by controlling the opening and closing timing of the intake control valves in accordance with rotation speed or load of the engine. As a result, an output of the engine is improved. It is also possible to reduce a pumping loss, which increases when the engine is operated under a partial load especially when the engine is idling, by controlling the opening and closing timing of the intake control valves in accordance with the rotation speed or the load of the engine. Thus, fuel consumption is reduced, as is commonly known. When the engine is operated under a partial load, especially when the engine is idling, intake air is drawn through one port alone. Therefore, swirls or tumbles are generated in the cylinder and atomization of fuel is improved. Accordingly, the fuel is mixed with air efficiently, and fuel combustion is improved.
Conventionally, a 90-degree rotating type rotary solenoid actuator, an R/S actuator, is used as an actuator that drives the intake control valve open or close. The R/S actuator holds the intake control valve at a neutral position where an intake passage is half opened, when the R/S actuator is not energized. When the R/S actuator is energized, the R/S actuator drives the intake control valve from the neutral position in a direction to open or to close the intake control valve in accordance with strength and direction of the energization.
In such a case in which the intake control system employs the R/S actuator that holds the intake control valve at the neutral position when the R/S actuator is not energized, safety is ensured because the engine is capable of operating without closing the intake passage even if the R/S actuator is not energized because of a breakdown and the like. In addition, the direction of opening and closing the intake control valve is switched by altering the direction of the energization. Therefore, the intake control valve is driven from a full opening position to a full closing position quickly, and vice versa.
However, the conventional intake control valve explained above has no means for detecting its valve opening degree, and therefore, the valve opening degree cannot be controlled precisely. The conventional intake control valve is regulated basically in only three positions, a full opening position, a neutral position and a full closing position. In addition to the intake control valves, an electronic throttle valve is disposed in upstream of a surge tank and is controlled by an electronic control unit (ECU). The ECU regulates the opening degree of the electronic throttle valve based on the signal of the rotation speed of the engine so that the rotation speed is generally constant even during the idling operation of the engine.
Thus, the conventional intake control system is not constructed to control the intake quantity for each cylinder. Therefore, the intake quantity varies among the cylinders, and therefore, the rotation speed of the engine fluctuates as shown in FIG. 5. In FIG. 5, the axis NE represents the rotation speed of the engine and the line RLL represents the lower limit rotation speed above which the engine is operable and the engine does not stall. The idling rotation speed of the engine is set based on an idling rotation speed of a cylinder having the lowest idling rotation speed, in order to prevent an engine stall. Therefore, the idling rotation speed is slightly too fast for the other cylinders. As a result, the fuel consumption is increased in the other cylinders.
It is therefore an object of the present invention to provide an intake control system of a multi-cylinder internal combustion engine, the intake control system being capable of reducing fuel consumption during an idling operation of the engine.
According to an embodiment of the present invention, an intake control system has intake control valves disposed in respective intake passages of cylinders, rotary solenoid actuators for respectively driving the intake control valves open or close, opening degree sensors for detecting opening degree of the intake control valves and an ECU. The ECU controls valve opening degree of the intake control valve for each cylinder based on signals from a crank angle sensor, a cylinder determination sensor, the opening degree sensor and the like. The intake control system regulates the valve opening degree of the intake control valves for each cylinder to converge an idling rotation speed of the engine to a lower limit rotation speed above which the engine is operable and the engine does not stall. Thus, the rotation speeds of the entire cylinders are converged to the lower limit rotation speed during the idling operation. As a result, the fuel consumption during the idling operation is reduced.